As an example of a connector for a pipe, patent document 1 discloses a connector comprising a connector body into which a pipe can be inserted, and a retainer that can be installed on the connector body.
Specifically, the retainer is positioned in a provisionally fastened position where the pipe can be inserted into the connector, and the positioning of the connector body is released by the insertion of the pipe, at which time, the retainer moves to a position for preventing the pipe from coming off, and prevents the pipe from coming off.
Here, a spring member (urging member) is provided between the connector body and the retainer, and the spring member moves the retainer having been released in positioning to the position for preventing the pipe from coming off, whereby it can be confirmed whether the pipe is connected in a properly connected position of the connector body.    Patent document 1: Japanese Unexamined Patent Publication No. 2006-105241